Conflictos Ambientales

The Solar Constant Since 1600

The graph above shows the solar irradiance (also called the solar constant) since The graph above shows the solar irradiance (also called the solar constant) since 1610. Although sensitive instruments were not available back in 1600 to make these 1610. Although sensitive instruments were not available back in 1600 to make these measurements, scientists have developed many techniques to 'reconstruct' the

measurements, scientists have developed many techniques to 'reconstruct' the irradianceirradiance values using

values using other astronomical other astronomical and geophysical and geophysical data. data. The thin The thin line in line in the graphthe graph indicates the annual solar irradiance, while the thick line shows the running average. It is indicates the annual solar irradiance, while the thick line shows the running average. It is plain to see that today's values are significantly higher than in centuries past. Some plain to see that today's values are significantly higher than in centuries past. Some scientists feel this accounts for global warming which has also increased, mostly since scientists feel this accounts for global warming which has also increased, mostly since 1800. The majority of scientists have concluded that solar increases only account for 1/2 1800. The majority of scientists have concluded that solar increases only account for 1/2 of the global warming since the 1970's, and significantly less than 1/2 in the 2000s.

of the global warming since the 1970's, and significantly less than 1/2 in the 2000s.

Problem 1

Problem 1 _{- Between 1645 and 1715, a period known as the Maunder Minimum, there- Between 1645 and 1715, a period known as the Maunder Minimum, there}

were few sunspots observed, and no 11-year sunspot cycle. It was a time of extremely were few sunspots observed, and no 11-year sunspot cycle. It was a time of extremely cold winters in Europe. What was the average solar insolation (Solar Constant) during cold winters in Europe. What was the average solar insolation (Solar Constant) during this time?

this time?

Problem 2

Problem 2 _{- What has been the average insolation during the period after 1950?- What has been the average insolation during the period after 1950?}

Problem 3

Problem 3 _{- What is the percent change in solar insolation between the Maunder- What is the percent change in solar insolation between the Maunder}

Minimum period and the time period after 1950? Minimum period and the time period after 1950?

Problem 4

Problem 4 _{- - Although some Although some global warming has global warming has been measured sbeen measured since 1800, the ince 1800, the mostmost}

dramatic change in global temperatures has

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Answer Key

Answer Key

Problem 1

Problem 1 _{- Between 1645 and 1715, a period known as the Maunder Minimum, there were- Between 1645 and 1715, a period known as the Maunder Minimum, there were}

few sunspots observed, and no 11-year sunspot cycle. It was a time of extremely cold winters few sunspots observed, and no 11-year sunspot cycle. It was a time of extremely cold winters in Europe. What was the average solar insolation (Solar Constant) during this time? Answer: in Europe. What was the average solar insolation (Solar Constant) during this time? Answer: The graph shows a pronounced minimum to the insolation with a value

The graph shows a pronounced minimum to the insolation with a value near 1,363.4 watts pernear 1,363.4 watts per square meter.

square meter.

Problem 2

Problem 2 _{- What has been the average insolation during the period after 1950? Answer:- What has been the average insolation during the period after 1950? Answer:}

Estimates near 1,366 watts per square meter

Estimates near 1,366 watts per square meter are acceptableare acceptable based on the trend in the data.based on the trend in the data.

Problem 3

Problem 3 _{- What is the percent change in solar insolation between the Maunder Minimum- What is the percent change in solar insolation between the Maunder Minimum}

period and the tim

period and the time period after 1950? e period after 1950? Answer: Answer: 100% x (1,366 100% x (1,366 - 1,363.4)/1,363.4 =- 1,363.4)/1,363.4 = 0.2%0.2% increase since the 1600s.

increase since the 1600s.

Problem 4

Problem 4 _{- - Although some Although some global warming global warming has been has been measured since measured since 1800, the 1800, the mostmost}

dramatic change in global temperatures has occurred since 1970. Based on the historical dramatic change in global temperatures has occurred since 1970. Based on the historical insolation derived from solar activity cycles, why do scientists who study climate change claim insolation derived from solar activity cycles, why do scientists who study climate change claim that solar changes do not

that solar changes do not account for the most recent temperature increases?account for the most recent temperature increases?

Answer: When the historical changes in solar insolation since 1600 are compared with global Answer: When the historical changes in solar insolation since 1600 are compared with global temperature changes, the significant increases measured since 1970 do not match up with the temperature changes, the significant increases measured since 1970 do not match up with the essentially 'flat' average insolation changes since the 1950's.

essentially 'flat' average insolation changes since the 1950's. This suggests to scientists that atThis suggests to scientists that at least since 1970, solar changes have been less responsible for global temperature rise than least since 1970, solar changes have been less responsible for global temperature rise than other factors. The most significant one that has been measured is the rise in carbon dioxide other factors. The most significant one that has been measured is the rise in carbon dioxide levels due to human activity.

levels due to human activity.

Teacher Note:

Teacher Note: _{Satellites were not available before the 1970's to accurately measure the solarSatellites were not available before the 1970's to accurately measure the solar}

constant every year, so scientists have devised a number of 'proxies' that they think correlate constant every year, so scientists have devised a number of 'proxies' that they think correlate with solar insolation changes. Once these proxies are verified using satellite data, they can be with solar insolation changes. Once these proxies are verified using satellite data, they can be used to extrapolate how the solar constant has changed in previous decades and centuries. used to extrapolate how the solar constant has changed in previous decades and centuries. The more of these proxy data bases scientists can correlate with solar insolation, the more The more of these proxy data bases scientists can correlate with solar insolation, the more accurate are the extrapolations back in time for the particular quantity they are historically accurate are the extrapolations back in time for the particular quantity they are historically studying.

studying.

For more about how scientists reconstruct solar insolation from past years, see the

For more about how scientists reconstruct solar insolation from past years, see the article by J.article by J. Lean, "Evolution of the Sun's Spectral Irradiance Since the Maunder Minimum" published in Lean, "Evolution of the Sun's Spectral Irradiance Since the Maunder Minimum" published in the Geophysical Research Letters, Vol. 27, No. 16, pp. 2425-2428 on Aug. 15, 2000.

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